Difference between RO and drinking water?

[ViciousFishes]

I have just started to cycle a 20gal. tank that will be for corals. I currently have a 125gal. FOWLR and have been using drinking water (purified water)for top-offs with no problems. I know corals are much more sensitive so what's the difference between drinking and RO water. I was talking to the water guy and he uses carbon blocks and micron filters to filter the water. This sounds just like those RO systems or RO/DI systems minus the DI filtering. The water purifiers they sell in home improvement stores also look to be identical to RO systems some even have RO in the name. An RO system is just not in the budget right now and im wondering if it's really that much different than what the water guy uses. Any help would greatly be appreciated.

Thanks,

George

 

[dralarms]

The DI part removes disolved solids, in other words metals & such. I think. I don't have an ro/di yet but they are selling on line (ebay) for right around $100.